Data scrambler generation of pseudo-random bit sequence for semi-stationary Q-mode signal

ABSTRACT

In a data communication system, a transmitter of a modem, for example, uses a single scrambler to operate in a data communication mode and in a non-data mode. During the data communication mode the scrambler is used to scramble data for communication by the transmitter. During the non-data mode, the scrambler is used to generate a non-data mode signal for communication by the scrambler. The modem may be an ADSL modem, for example, in which case the data communication mode is SHOWTIME while the non-data mode may be Q-mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 09/906,410, filed Jul. 16, 2001, the complete subject matter ofwhich is hereby incorporated herein by reference in its entirety.

This application makes reference to, and claims priority to and thebenefit of, U.S. provisional application Ser. No. 60/241,126 filed Oct.16, 2000.

INCORPORATION BY REFERENCE

The above-referenced U.S. provisional application Ser. No. 60/241,126 ishereby incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

BACKGROUND OF THE INVENTION

Current ADSL modem system designs do not incorporate a low powertransmission mode. Such systems require high power dissipation in themodem line driver, even when no data is being transmitted.

Accordingly, ITU contributions have proposed a low power mode (i.e.,“Q-mode,”) in the transmitter. During the proposed Q-mode, the modem isstill in the ready state, but enters a low power mode during periods ofno data transmission.

One ITU contribution, HC-029R1, formally defines a semi-stationaryQ-mode signal, that employs a pair of pseudo-random bit sequence(“PRBS”) generators, each with a period of greater than 4000. Oneproblem with this proposal, however, is that the receiver would requiresynchronization to two PRBS generators. In addition, requiring two PRBSgenerators as such correspondingly requires additional hardware in themodem, as well as additional overhead associated with the overallsystem. Moreover, during the non-Q-mode periods of operation, i.e.,during data mode or “SHOWTIME,” the two PRBS generators sit idle.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present invention may be found in communication systemhaving a data communication node. The data communication node may be,for example, a modem (such as an ADSL modem). The data communicationnode in turn has a transmitter, which itself has a scrambler.

The transmitter uses the scrambler to operate in two modes. The firstmode is a data communication mode, which, in the case when the datacommunication node is an ADSL modem, is SHOWTIME. During the datacommunication mode, the scrambler is used to scramble data that iscommunicated by the transmitter.

The second mode is a non-data mode, which in the case when the datacommunication node is an ADSL transmitter, may be Q-mode. During thenon-data mode, the scrambler is used to generate a non-data mode signal.

In one embodiment of the invention, a determination is made whether datais present at one or more inputs to the system. If it is determined thatdata is present, a determination is then made whether the scrambler isconfigured for the data communication mode. If it isn't, the scrambleris configured for the data communication mode, and the system operatesin that mode. If it is indeed configured for the data communicationmode, then the system simply operates in that mode.

If it is determined that no data is present, a determination is thenmade whether the scrambler is configured for the non-data mode. If itisn't, the scrambler is configured for the non-data mode, and the systemoperates in that mode. If it is indeed configured for the non-data mode,then the system simply operates in that mode.

In one embodiment of non-data mode operation, a non-data mode input tothe scrambler is selected. A non-data mode signal is then generated,using a first output of the scrambler. Next, the non-data mode signal isoutput, using a second output of the scrambler, for communication by thetransmitter. This process is repeated for successive outputs of thescrambler, for as long as the non-data mode input to the scrambler isselected.

These and other advantages and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of a generic communication system that may beemployed in connection with the present invention.

FIG. 2 is a functional block diagram of an ADSL modem transmitteraccording to the present invention.

FIG. 3 is a schematic block diagram illustrating one embodiment by whichthe scrambler of FIG. 2 performs the two functions shown in FIG. 2.

FIG. 4 is a block diagram of one embodiment of Q-mode signal generationcircuitry in accordance with the present invention.

FIG. 5 illustrates a more detailed embodiment of the Q-mode signalgeneration circuitry of FIG. 4.

FIG. 6 is a flow diagram of overall control for mode selection inaccordance with the present invention.

FIG. 7 is a depiction of a generic scrambler that may be employed inconnection with the present invention.

FIG. 8 is one specific embodiment of a scrambler that may be employed inconnection with the present invention.

FIG. 9 is a scrambler based on the scrambler of FIG. 8 but withalternate outputs selected in such a way that two separate outputstreams are produced.

FIG. 10 is a depiction of a generic PRBS generator in accordance withthe present invention.

FIG. 11 is one specific embodiment of the PRBS generator of FIG. 10 inaccordance with the present invention.

FIG. 12 is a PRBS generator based on the PRBS generator of FIG. 11, butwith alternate outputs selected in such a way that two separate outputstreams are produced, in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of a generic communication system that may beemployed in connection with the present invention. The system comprisesa first communication node 101, a second communication node 111, and achannel 109 that communicatively couples the nodes 101 and 111. Thecommunication nodes may be, for example, ADSL modems or any other typeof transceiver device that transmits or receives data over a channel.The first communication node 101 comprises a transmitter 105, a receiver103 and a processor 106. The processor 106 may comprise, for example, amicroprocessor. The first communication node 101 is communicativelycoupled to a user 100 (e.g., a computer) via communication link 110, andto the channel 109 via communication links 107 and 108.

Similarly, the second communication node 111 comprises a transmitter115, a receiver 114 and a processor 118. The processor 118, likeprocessor 106, may comprise, for example, a microprocessor. The secondcommunication node 111 is likewise communicatively coupled to a user 120(again a computer, for example) via communication link 121, and to thechannel 109 via communication links 112 and 113.

During operation, the user 100 can communicate information to the user120 using the first communication node 101, the channel 109 and thesecond communication node 111. Specifically, the user 100 communicatesthe information to the first communication node 101 via communicationlink 110. The information is transformed in the transmitter 105 to matchthe restrictions imposed by the channel 109. The transmitter 105 thencommunicates the information to the channel 109 via communication link107. The receiver 114 of the second communication node 111 nextreceives, via communication link 113, the information from the channel109 and transforms it into a form usable by the user 120. Finally, theinformation is communicated from the second communication node 111 tothe user 120 via the communication link 121.

Communication of information from the user 120 to the user 100 may alsobe achieved in a similar manner. In either case, the informationtransmitted/received may also be processed using the processors 106/118.

FIG. 2 is a functional block diagram of an ADSL modem transmitteraccording to the present invention. A transmitter 201 comprises ascrambler 203 and control 205. Control 205 causes the transmitter 201 tooperate in two different modes, namely a data transmission or “SHOWTIME”mode (designated functionally by block 207) and a non-data mode or“Q-mode” (designated functionally by block 209). The non-data mode maybe, for example, a quiescent, low power mode. While a switch 211 isshown in FIG. 2 as selecting between the data and non-data modes, theswitch 211 is not necessarily a hardware switch per se, but rather anabstract selection mechanism, as explained more completely below.

FIG. 3 is a schematic block diagram illustrating one embodiment by whichthe scrambler of FIG. 2 performs the two functions shown in FIG. 2.Similar to control 205 of FIG. 2, control 301 acts as a selector betweenQ-mode operation and data operation. In Q-mode, control 301 selects “1”as the input to scrambler 303, employs the scrambler 303 output forQ-mode purposes, and selects the Q-mode signal as the output ofmultiplexor 305.

In data mode, control 301 selects the input of scrambler 303 to beunscrambled data, employs the output of the scrambler 303 to bescrambled data, and selects the data mode signal as the output ofmultiplexor 305. In either mode, the output of multiplexor 305 is sentto a line driver (not shown).

As can be appreciated from FIGS. 2 and 3, a single scrambler is used toscramble the data during data transmission and to control the generationof the Q-mode signal.

FIG. 4 is a block diagram of one embodiment of Q-mode signal generationcircuitry in accordance with the present invention. When Qmode isselected (i.e., “1” at the input of scrambler 401), the scrambler 401switches between generating the Q-mode signal and outputting the Q-modesignal. More specifically, for each symbol of the Q-mode signal, twosuccessive outputs from the scrambler 401 are used. The first outputselects whether the basic symbols (i.e., S1 and S2) or their inversesshould be generated. In the embodiment of FIG. 4, if the first output is“0,” then S1 and S2 are presented at the input of multiplexor 403. Ifinstead the first output is “1,” then the inverse of S1 and S2 arepresented at the inputs of multiplexor 403.

The second output of scrambler 401 is then presented to control 405,which selects the output of the multiplexor 403. The output ofmultiplexor 403 represents the Q-mode signal.

FIG. 5 illustrates a more detailed embodiment of the Q-mode signalgeneration circuitry of FIG. 4. A scrambler 501 with its input clampedto one generates an output sequence of bits at a rate equal to twice thesymbol rate of the system. The outputs of the scrambler 501 arealternately connected to a first input 505 and a second input 507 bymeans of a switch 503. The first input 505 is used by multiplier 513 toeither invert or not invert (i.e. multiply by +1 or −1) a stationarysignal 509 resulting in a first signal 514. The same first input 505also is used by multiplier 515 to either invert or not invert anon-stationary signal 511, resulting in a second signal 516. The firstsignal 514 and the second signal 516 form the inputs to a multiplexor517.

The second input 507 is applied to the input of a serial-to-parallelconvertor 531 that converts groups of bits from the second input 507 toa first 8-bit integer 535. A duty cycle 533 (i.e. a positive numberbetween 0 and 1) is scaled in scaler 534 to an 8-bit positive integer(i.e., an integer between 0 and 255 inclusive) to produce a second 8-bitinteger 537. A comparator 539 produces an output 518 that is 1 wheneverthe first 8-bit integer 535 is less than the second 8-bit integer 537;the output 518 is 0 otherwise. The output 518 is the select input 519 ofmultiplexor 517. The output of multiplexor 517 is Q-mode signal 521,which is comprised of first signal 514 whenever the select input 519 is“1,” and second signal 516 whenever the select input 519 is “0.”

A final multiplexor 525, operating under control of Q-mode enable 527,has an output signal 529 that is Q-mode signal 521 whenever Q-modeenable 527 is 1; the output signal 529 is the data mode signal 523whenever Q-mode enable 527 is “0.” Subsequent processing stages in theADSL transmitter convert the output signal 529 into a signal that istransmitted by the ADSL transmitter.

FIG. 6 is a flow diagram of overall control for mode selection inaccordance with the present invention. First, inputs to the system areexamined (block 601). “Inputs” may be, for example, user data,internally generated overhead data (e.g., system status or commands),etc., or no data at all. If it is determined that data is present at theinputs (block 603), then a determination is made whether the system isin the data mode (block 605). If the system is indeed in the data mode,the system simply operates in the data mode (block 607). If it is not inthe data mode (as determined at block 605), the system first configuresthe scrambler for data mode operation (block 609), and then operates inthe data mode (block 607).

If, on the other hand, it is determined that no data is present at theinputs (block 603), then a determination is made whether the system isin Q-mode (block 611). If the system is indeed in Q-mode, the systemsimply operates in Q-mode (block 613). If it is not in Q-mode (asdetermined at block 611), the system first configures the scrambler forQ-mode operation (block 615), and then operates in Q-mode (block 613).

FIG. 7 is a depiction of a generic scrambler that may be employed inconnection with the present invention. Scrambler 701 outputs a pseudorandom bit sequence with a period of 2^(N)−1, where each of j₁, j₂, . .. j_(N) comprises one of “0” or “1” and {j₁, j₂, . . . j_(N)} (not allequal to “1”) represents the initial state of the scrambler 701. {c₁, c₂. . . c_(N)} represents the coefficients of a primitive polynomial.

FIG. 8 is one specific embodiment of the scrambler of FIG. 7 that may beemployed in connection with the present invention. Scrambler 801 isdefined for ADSL data transmission in G.992.1 and G.992.2. The scrambler801 of FIG. 8 is based on the primitive polynomial 1⊕x⁻¹⁸ ⊕x⁻²³ with the⊕ symbol used to denote addition mod 2. When the scrambler 801 input isclamped to “1,” the scrambler 801 output becomes a pseudo-random bitsequence with a period of 2²³−1.

To consider the randomness qualities of the scrambler of FIG. 8, let thesequence {a_(j), a_(j+1), a_(j+2), . . . } represent the output sequenceemitted by the scrambler with its input clamped to one where j is anarbitrary integer representing time. Assume further that the initialstate of the scrambler is {a_(j+1), a_(j+2), . . . , a_(j+23)} for somej. Then subsequent outputs of the scrambler are defined by the aboveprimitive polynomial to bea_(i)=1⊕a_(i−18)⊕a_(i−23) for all integer values of i.  (1)Equivalently,a_(i)⊕a_(i−18)⊕a_(i−23)=1,  (2)it being understood that binary arithmetic is being used.

Equation (2) expresses the fundamental recurrence relation for thescrambler of FIG. 8. Further properties of this scrambler make itattractive for generating pseudo-random sequences. Of course, a wholefamily of scramblers can be defined in a similar way.

Consider the structure of scrambler 901 of FIG. 9, which is based on thescrambler of FIG. 8 but with alternate outputs selected in such a waythat two separate output streams are produced. To determine therandomness properties of the resulting subsequences, let {b_(i)}represent the output sequence obtained by selecting the even-numberedoutputs of the master scrambler. That is, letb_(i)=a_(2i) for all i.  (3)It is asserted that the {b_(i)} sequence defined by (3) also satisfiesEquation (2), which means that {b_(i)} is also a PRBS sequence with allthe properties possessed by the {a_(j)} sequence. That is, it isasserted thatb_(i)⊕b_(i−18)⊕b_(i−23)=1.  (4)Substituting (3) into (4), the assertion is thata_(2i)⊕a_(2i−36)⊕a_(2i−46)=1.  (5)To prove this assertion, note that from (1) we know that $\begin{matrix}{{a_{2i} = {1 \oplus a_{{2i} - 18} \oplus a_{{2i} - 23}}},\begin{matrix}{a_{{2i} - 18} = {1 \oplus a_{{({{2i} - 18})} - 18} \oplus a_{{({{2i} - 18})} - 23}}} \\{= {1 \oplus a_{{2i} - 36} \oplus a_{{2i} - 41}}}\end{matrix}} & (6)\end{matrix}$from whicha_(2i−36)=1⊕a_(2i−18)⊕a_(2i−41)  (7)Also from (1), $\begin{matrix}\begin{matrix}{a_{{2i} - 23} = {1 \oplus a_{{({{2i} - 23})} - 18} \oplus a_{{({{2i} - 23})} - 23}}} \\{= {1 \oplus a_{{2i} - 41} \oplus a_{{2i} - 46}}}\end{matrix} & \quad\end{matrix}$from whicha_(2i−46)=a_(2i−23)⊕a_(2i−41.)  (8)Substituting (7) and (8) into the left-hand side of (5) we have$\begin{matrix}{{a_{2i} \oplus 1 \oplus a_{{2i} - 18} \oplus a_{{2i} - 41} \oplus 1 \oplus a_{{2i} - 23} \oplus a_{{2i} - 41}} = {a_{2i} \oplus a_{{2i} - 18} \oplus a_{{2i} - 23}}} & {{{~~~~~~~~~~~~~~}\quad}(9)} \\{= 1} & {(10)}\end{matrix}$from (2) with i replaced by 2i. The chain of implications just navigatedshows thatb_(i)⊕b_(i−18)⊕b_(i−23)=1  (4)as was asserted. Therefore, the sequence, {b_(i)} obtained by selectingthe even-numbered outputs of the master scrambler is, itself, a PRBSsequence with the same randomness properties as that of the masterscrambler. A similar argument proves that the sequence obtained byselecting the odd-numbered outputs of the master scrambler also is aPRBS sequence with the same randomness properties as the masterscrambler.

An embodiment with exactly similar properties (except that the bitsequence is inverted) obtains when a PRBS generator is substituted forthe scrambler. FIG. 10 is a depiction of a generic PRBS generator thatmay be employed in connection with the present invention. PRBS generator1001 outputs a pseudo random bit sequence with a period of 2^(N)−1,where each of i₁, i₂, . . . i_(N) comprises one of “0” or “1” and {i₁,i₂, . . . i_(N)} (not all equal to “0”) represents the initial state ofthe PRBS generator 1001. {c₁, c₂ . . . c_(N)} represents thecoefficients of a primitive polynomial.

FIG. 11 is one specific embodiment of the PRBS generator of FIG. 10 inaccordance with the present invention. The PRBS generator 1101 of FIG.11 is based on the same polynomial as that upon which FIG. 8 is based.To consider the randomness qualities of FIG. 11, let the sequence{a_(j), a_(j+1), a_(j+2), . . . } represent the output sequence emittedby the PRBS where j is an arbitrary integer representing time. Assumefurther that the initial state of the generator is {a_(j+1), a_(j+2), .. . , a_(j+23)} for some j. Then subsequent outputs of the PRBSgenerator are defined by the above primitive polynomial to bea_(i)=a_(i−18)⊕a_(i−23) for all integer values of i.  (1)Equivalently,a_(i)⊕a_(i−18)⊕a_(i−23)=0,  (2)it being understood that binary arithmetic is being used.

Equation (2) expresses the fundamental recurrence relation for the PRBSgenerator. Further properties of. this PRBS generator make it attractivefor generating pseudo-random sequences. Of course, a whole family ofPRBS generators can be defined in a similar way.

Consider the structure of PRBS generator 1201 of FIG. 12, which is basedon the PRBS generator of FIG. 11, but with alternate outputs selected insuch a way that two separate output streams are produced (in accordancewith the present invention). To consider the randomness qualities of thescrambler 1201 of FIG. 12, let {b_(i)} represent the output sequenceobtained by selecting the even-numbered outputs of the master PRBSgenerator. That is, letb_(i)=a₂₁ for all i.  (3)It is asserted that the {b₁} sequence defined by (3) also satisfiesEquation (2), which means that {b_(i)} is also a PRBS sequence with allthe properties possessed by the {a_(i)} sequence. That is, it isasserted thatb_(i)⊕b_(i−18)⊕b_(i−23)=0.  (4)Substituting (3) into (4), the assertion is thata_(2i)⊕a_(2i−36)⊕a_(2i−46)=0.  (5)To prove this assertion note that from (1) we know that $\begin{matrix}{{a_{2i} = {a_{{2i} - 18} \oplus a_{{2i} - 23}}},\begin{matrix}{a_{{2i} - 18} = {a_{{({{2i} - 18})} - 18} \oplus a_{{({{2i} - 18})} - 23}}} \\{= {a_{{2i} - 36} \oplus a_{{2i} - 41}}}\end{matrix}} & (6)\end{matrix}$from whicha_(2i−36)=a_(2i−18)⊕a_(2i−41)  (7)Also from (1), $\begin{matrix}{a_{{2i} - 23} = {a_{{({{2i} - 23})} - 18} \oplus a_{{({{2i} - 23})} - 23}}} \\{= {a_{{2i} - 41} \oplus a_{{2i} - 46}}}\end{matrix}$from whicha_(2i−46)=a_(2i−23)⊕a_(2i−41)  (8)Substituting (6), (7), and (8) into the left-hand side of (5) we have$\begin{matrix}\begin{matrix}{{a_{2i} \oplus a_{{2i} - 18} \oplus a_{{2i} - 41} \oplus a_{{2i} - 23} \oplus a_{{2i} - 41}} = {a_{2i} \oplus a_{{2i} - 18} \oplus a_{{2i} - 23}}} \\{= \begin{matrix}0 & (10)\end{matrix}}\end{matrix} & (9)\end{matrix}$from (2) with i replaced by 2i. The chain of implications just navigatedshows thatb_(i)⊕b_(i−18)⊕b_(i−23)=0  (4)as asserted. Therefore, the sequence, {b_(i)}, obtained by selecting theeven-numbered outputs of the master PRBS generator is, itself, a PRBSsequence with the same randomness properties as that of the master PRBSgenerator. A similar argument proves that the sequence obtained byselecting the odd-numbered outputs of the master PRBS generator also isa PRBS sequence with the same randomness properties as the master PRBSgenerator.

Many modifications and variations of the present invention are possiblein light of the above teachings. Thus, it is to be understood that,within the scope of the appended claims, the invention may be practicedotherwise than as described hereinabove.

1. A communication system comprising: a data communication node; and atransmitter located in the data communication node, the transmitterhaving a scrambler, the transmitter using the scrambler to operate in afirst, data communication mode and in a second, non-data mode.
 2. Thedata communication system of claim 1 wherein the data communication nodecomprises an ADSL modem.
 3. The data communication system of claim 2wherein the first, data communication mode comprises SHOWTIME.
 4. Thedata communication system of claim 3 wherein the scrambler scramblesdata during SHOWTIME.
 5. The data communication system of claim 2wherein the second, non-data mode comprises a Q-mode.
 6. The datacommunication system of claim 5 wherein the scrambler at least partiallygenerates a Q-mode signal.
 7. The data communication system of claim 1wherein the scrambler scrambles data during the first, datacommunication mode.
 8. The data communication system of claim 1 whereinthe scrambler at least partially generates a non-data mode signal.
 23. Acommunication system comprising: a transmitter capable of: determiningthat data is not present at at least one input to the transmitter;determining whether the transmitter is configured for a non-data mode;configuring the transmitter for the non-data mode if a determination ismade that the transmitter is not configured for the non-data mode; andoperating in the non-data mode.
 24. The communication system of claim 23further comprising being capable of: determining whether the transmitteris configured for a data communication mode; configuring the transmitterfor the data communication mode if a determination is made that thetransmitter is not configured for the data communication mode; operatingin the data communication mode;
 25. The communication system of claim 23wherein operating in the non-data mode comprises generating, at leastpartially, a non-data signal.
 26. The communication system of claim 24wherein operating in the data communication mode comprises scramblingdata received at the at least one input.
 27. The communication system ofclaim 24 wherein the transmitter is located in an ADSL modem.
 28. Thecommunication system of claim 27 wherein the data communication modecomprises SHOWTIME.
 29. The communication system of claim 28 whereinoperating in the data communication mode comprises scrambling dataduring SHOWTIME.
 30. The communication system of claim 27 wherein thenon-data mode comprises a Q-mode.
 31. The communication system of claim30 wherein operating in the non-data mode comprises generating, at leastpartially, a Q-mode signal.
 32. A communication system comprising: atransmitter being capable of: generating, using a first output of twosuccessive outputs, a non-data mode signal; and controlling, using asecond output of said two successive outputs, the output of the non-datamode signal.
 33. The communication system of claim 32 further beingcapable of selecting a non-data mode input.
 34. The communication systemof claim 33 further comprising being capable of repeating the generatingand controlling for as long as the non-data mode input is selected. 35.The communication system of claim 32 further comprising the transmitterbeing capable of: selecting a data communication mode input; andscrambling data received for communication.
 36. The communication systemof claim 35 wherein the transmitter is located in an ADSL modem.
 37. Thecommunication system of claim 36 wherein the data communication modecomprises SHOWTIME.
 38. The communication system of claim 36 wherein thenon-data mode comprises a Q-mode.
 39. A method of operating atransmitter in a data communication system, the method comprising:determining that data is not present at at least one input; determiningwhether the transmitter is configured for a non-data mode; configuringthe transmitter for the non-data mode if a determination is made thatthe transmitter is not configured for the non-data mode; and operatingin the non-data mode.
 40. The method of claim 39 further comprising:determining that data is present at the least one input; determiningwhether the transmitter is configured for a data communication mode;configuring the transmitter for the data communication mode if adetermination is made that the transmitter is not configured for thedata communication mode; and operating in the data communication mode.41. The method of claim 40 wherein operating in the data communicationmode comprises scrambling data received at the at least one input. 42.The method of claim 39 wherein operating in the non-data mode comprisesgenerating, at least partially, a non-data signal.
 43. The method ofclaim 40 wherein the transmitter is located in an ADSL modem.
 44. Thedata communication system of claim 43 wherein the data communicationmode comprises SHOWTIME.
 45. The data communication system of claim 44wherein operating in the data communication mode comprises scramblingdata during SHOWTIME.
 46. The data communication system of claim 43wherein the non-data mode comprises a Q-mode.
 47. The data communicationsystem of claim 46 wherein operating in the non-data mode comprisesgenerating, at least partially, a Q-mode signal.
 48. A method ofoperating a transmitter in a data communication system, the methodcomprising: generating, using a first output of two successive outputs,a non-data mode signal; and controlling, using a second output of saidtwo successive outputs, the output of the non-data mode signal.
 49. Themethod of claim 46 further comprising selecting a non-data mode input.50. The method of claim 49 further comprising repeating the generatingand controlling for as long as the non-data mode input is selected. 51.The method of claim 49 further comprising: selecting a datacommunication mode input; and scrambling data received forcommunication.
 52. The method of claim 51 wherein the transmitter islocated in an ADSL modem.
 53. The data communication system of claim 52wherein the data communication mode comprises SHOWTIME.
 54. The datacommunication system of claim 52 wherein the non-data mode comprises aQ-mode.